Long scale electrical instruments



May 6, 1958 A. L. NYLANDER [LONG SCALE ELECTRICAL INSTRUMENTS 2 Sheets-Sheet 1 Filed May 26. 1953 Fig.

Fig.3.

Fig.4.

Inventor: ATnold L. Nylander;

His Attor ney.

y 1953 A. L; NYLANDER 2,833,989

LONG SCALE ELECTRICAL INSTRUMENTS Filed May 26. 1953 2 Sheets-Sheet 2Inventor: Arnold L. Nylahder, y WMMGT -His Attorney.

LONG SCALE ELECTRICAL INSTRUMENTS" Arnold-L. Nylauder, Swampscott, Mass,assignor to General 'El e'ctric Company, a corporation oiNew YorkApplication May 26,1953, Serial-N0.--357,6 15

4 Claims. (Cl. 324'-'150) My invention relates to improvements inlong-scale atent electrical instruments, and its' chief objectis'toprovide instruments having greater sensitivity and much lowermanufacturing cost than those previously" available. Other objects andadvantages will appear asthe' description proceeds;

Brieflystated, in accordance with one aspect ofmy invention; I provideimproved instruments-having permanent magnets whioh'are magnetized in'asingle"strai ght line direction. This makes practical the-use 'oforiented perm'anent'magnet materials having a preferreddirectionofmagnetization, which, when magnetized inth' eir preferred direction;possess exceptionally high" values of coercive force and residualmagnetism. Consequently, highvalues at magnetic flux'density are obtained'atlow cost, and these high'flux' densities givegre-ater'sensitivity" and improve other characteristics of theinstruments. Furthermore, magnetizing the magnets and adjustiug'thei rstrength for calibration purposes arefacil-itatedby"straight linemagnetization; which reduces manufacturing'costs. An even'greater' costreduction results from the'fact that my improved instruments do notrequire permanent rrra'gnets having complex shapes or'precisedimensions; which would necessitate costly 'grindingioperations, since"the common high-strength permanent magnet materials gen'-" erallycannot be machined by standard metal-working tools. Instead, my improved'instruments'cornprise pole piecesand a yoke which are preferablyprecisionmoulded of powdered iron, whereby precise shapes anddimensions"are obtained at low cost. My invention" has reducedithe manufacturingcost of the. magnet and polepiecestruo ture of one type instrument.to'one-third the previous cost; and. at the same time hasimpr-oved thesensitivity andother characteristics of the instrument.

My invention will be better understood from the fol lowing description.taken in connection with'th'e accompanying drawings, and its 'scope-will be pointed out in the appended claims. To. improve the clarity ofthe drawings ,and description, certain conventional parts, such as theinstrument case, calibrated scale, and electricalterminals, have beenomitted, since it is believed that those skilled in the art willhave nodifficulty in supp-lying such parts. In the drawings,

Fig. 1 is a plan view of an electrical instrument mechanism embodyingprinciples of my invention,

Fig. 2 is a section taken general-1y along the line 2--2 of Fig. 1,

Fig. .3 is-a plan View of another electrical instrument mechanismembodying principles of my invention,

Fig. 4 is an end view of the mechanism shown in Fig. 3,

Fig. 5 is a plan view of still another electrical instrument mechanismembodying principles of my invention,

Fig. 6 is a section taken generally along the line 66 of Fig. 5,

Fig. 7 is a plan view of still another electrical instrument mechanismembodying principles of my invention,

and

we a ICC.

Fig. 8 is a section taken generally along the line 8--8 of Fig.7.

Referring now to Figs. 1 and 2 of the drawings, the instrument mechanismcomprises a substantially annular inner pole piece 1 and an outer polepiece 2 having a C- shaped inner pole face which is substantiallyconcentric with the inner polejpiece. A' conventional moving coil 3ismounted so that 'a 'portion" of'the coil is movable along the circularair gap between the inner and outer pole 'pie'ces,'as is usual inlong-scale electrical instruments. Coil 3 is attached toa rotatableshaft 4 pivoted in conventional jewels Sand 6; The'jewels' may besupported by 'a bracket 7 extending inwardly from annular pole piece 1.Electricalconnections'tocoil' 3 are'made through conventional lea-'dinspirals Sand 9. A pointer 10'wl1ich'co'op'erates with" a calibratedscale', notshown, moveswith coil 3 and'shaft 4 to display't-he-v-alne'of current flowing through the'coil. Bias torquetending toreturn the pointer to its zero current position maybe supplied by thelead inspirals 8 and "9 in the'conventional manner.

A substantially annular yoke- 11 extends"circumferential-ly around theouter pole-piece- 2,"but.not"in"direct contact therewith. Yoke 11 has aninwardly extending tongue portion 12, to which "the" inner pole'piec'e-l is directly connected by suitable means such as" screw" 13'.The pole piece 1 may have a smallradialslot,f'asshowh in. Fig. 1, tofacilitate insertion of the. coil" 3 durin-gas portions'of' pole piece*1 on opposites-ides 'ofthisra' 'dial" slot. 7

Permanentmagnets 14 and 15' are'bonn'ected b'e'twe'e'n magnetspreferably has'substantially the-shaped a teetangular"parallelepiped;Preferably, the't'wo magnetsare located on diametrically opposite sidesof"polepiece"2,

as shown, andare respectively magnetized" iu"oppositef strai'gh'tflinedirections. In the clrawiiigs, the'lettersN' and S"respec'tively'represent 'north and? south'poles of the magnets. The magnets 14 and '15"provide "magnetic whicha portion of coil 3 moves,"throu'g"h pole piece1 can bemade of any suitable ferromagnetic materiaL such' assoftirn oranne'ale'd'steel, they" arepreferably'made of precision mouldedpowderediron. When" sofmade,

these parts can be shaped and dimensioned very precisely,"

thus providing a high quality instrument, with very low manufacturingcost. The pennanent'magnets" 14 and 15 -are"preferably made of oriented"permanent ma net mater'ial having extremely high coercive force andresidual" magnetism. For example, permanent ma 'rretaubys of thei'oriented Alnicotype may be usedi Because "oftheir rectangular shape,and the fact thatlittleifany grinding is required, 'these permanentma'gnetscanbe -madeait rue; ti've1y"'low"co'st.' The'out'er polepiece 2andthe yoke 11 may 'be placed in a suitable] jig, to holdthempreci'sely' in '.th"desired'relative position] i nets may then bebonded betweerirthe"outf'pole piece and the yoke to form a permanentunitary structure. This structure is then removed from the jig, and theother parts of the instrument are assembled.

Figs. 3 and 4 show a modified form of the instrument mechanism. Theinstrument shown in Figs. 3 and 4 is similar to that shown in Figs. 1and 2, except that the yoke and the permanent magnets are somewhatdifferently shaped. The yoke 16 is substantially Cshaped, as shown, withthe tongue portion '17 extending inwardly from its the permanent thaga)center. The permanent magnets 18 and 19 are shaped substantially liketruncated wedges, as shown. This wedge-like shape of the magnet permitsintimate magnetic joints while still maintaining pole piece 2 in acentral position, even though the thickness of individual magnets mayvary considerably. This construction increases the coil flux andmaintains a uniform circular air gap with resulting advantages ininstrument sensitivity and scale markings.

Figs. 5 and 6 show still another form of instrument which may be usedwhere small radial dimensions are required. The annular inner pole pieceis substantially the same as the inner pole pieces shown in thepreceding figures. The outer pole piece 21 is substantially C-shaped, asshown. The yoke comprises an annular portion 22 and a tongue portion 23.The annular portion 22 is coaxial with, and spaced axially apart from,the pole piece 21. The tongue 23 extends parallel to the common axis ofthe annular portion and the pole pieces. The inner pole piece 20 isconnected directly to tongue portion 23 by suitable means, such as screw24. A C-shaped permanent magnet 25 is connected between pole piece 21and the annular portion 22 of the yoke, as shown. C- shaped magnet 25 ismagnetized in a direction parallel to its axis, so that it providesmagnetic fiux through pole piece 21, across the air gap in which aportion of coil 26 moves, through pole piece 20, and back through tongue23 and annular portion 22. of the yoke.

Figs. 7 and 8 show another form of improved instrument mechanism havinga simple, inexpensive construction with external pivots. The moving coil29 has a low resistance because of its short mean length of turmmakingthis construction particularly useful in those applications(millivoltmeters) requiring low resistance. The substantially C-shapedyoke 27 and the substantially annular inner pole piece 28 may be mouldedas a single unitary part. A portion of a coil 29 is movable along an airgap between the inner pole piece 28 and an outer pole piece 30 having asubstantially C-shaped inner pole face. The moving coil is supported bypivots 31 and 32 which cooperate with conventional jewels, not shown,attached to the instrument frame. Conventional lead-in spirals are shownat 33 and 34. Permanent magnets 35 and 36, preferably shapedsubstantially like truncated Wedges, are connected between the yoke 27and the outer pole piece 30, as shown. This provides magnetic flux fromthe north poles of permanent magnets 35 and 36 through the outer polepiece 30, across the air gap to inner pole piece 28, and back throughyoke 27 to the south poles of the permanent magnets.

In all the embodiments described, it will be noted that the permanentmagnets are substantially straight in their direction of magnetization,and that all of the permanent magnets are magnetized in a singlestraight-line direction, so that the magnetic lines of flux aresubstantially straight and parallel as they pass through the permanentmagnets. As has been explained, this makes practical the use of orientedpermanent magnet materials, with consequent advantages in greatersensitivity and improved instrument characteristics.

It will be understood that my invention is not limited to the specificembodiments herein illustrated and described, and that the followingclaims are intended to cover all changes and modifications which do notdepart from the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters- Patent of theUnited States is;

1. In a long-scale electrical instrument of the moving coil type thecombination of a substantially annular inner pole piece, an outer polepiece having a C-shaped inner pole face substantially concentric withsaid inner pole piece, a C-shaped yoke extending about a portion of saidouter pole piece but not in direct contact therewith, said yoke having atongue portion extending inwardly from its center, means connecting saidinner pole piece direotly to said tongue portion, and a pair ofpermanent magnets connected between said yoke and said outer pole piece,said magnets each having substantially the shape of a truncated wedge,said pair of magnets being respectively located on diametricallyopposite sides of said outer pole piece and being respectivelymagnetized in opposite straight-line directions to provide magnetic fluxbetween said pole pieces, each of said magnets having pole faces of likepolarity in juxtaposition to the pole face of said outer pole piece.

2. In a long-scale electrical instrument of the moving coil type thecombination of a substantially annular inner pole piece, an outer polepiece having an outer pole face and a C-shapcd inner pole facesubstantially concentric with said inner pole piece and spaced therefromto form an air gap, a ferromagnetic yoke member connected to said innerpole piece and having portions thereof spaced radially outwardly fromportions of said outer pole piece, and a pair of wedge-shaped permanentmagnets connected between said outer pole piece portions and said yokeportions, said pair of magnets being respectively located ondiametrically opposite sides of said outer pole piece and beingsymmetrically aligned with and on diametrically opposite sides of saidannular inner pole piece, said magnets being respectively magnetized inopposite straightline directions to provide magnetic flux between saidpole pieces, each of said magnets having pole faces of like polarity injuxtaposition to the outer pole face of said outer pole piece portions.

3. In a long-scale electrical instrument of the moving coil type thecombination of a substantially annular inner pole piece, an outer polepiece having an outer pole face and a C-shaped inner pole facesubstantially concentric with said inner pole piece and spaced therefromto form an air gap, at substantially C-shaped ferromagnetic yoke memberhaving a centrally located inwardly extending tongue portion to whichsaid inner pole piece is connected and having portions which are spacedfrom portions of said outer pole piece, and a pair of wedge-shapedpermanent magnets connected between said outer pole piece portions andsaid yoke portions, said pair of magnets being respectively located ondiametrically opposite sides of said outer pole piece and beingrespectively magnetized in opposite straight-line directions to providemagnetic flux between said pole pieces, each of said magnets having polefaces of like polarity in juxtaposition to the outer pole face of saidouter pole piece portions.

4. The combination defined by claim 3 in which said yoke is in the formof a moulded powdered iron member and said inner pole piece is formed asan integral portion vthereof.

References Cited in the file of this patent UNITED STATES PATENTS2,586,831 Knudsen Feb. 26, 1952 FOREIGN PATENTS 787,424- France Sept.23, 1935

